This invention relates to intumescent compositions and more particularly to intumescent compositions comprising a bicyclic phosphate compound and a compound of nitrogen. The intumescent compositions of this invention impart flame retardant and intumescent character to polymers.
Intumescent compositions may be generally described as those compounds and mixtures which swell upon heating to produce a voluminous char or residue. A familiar example of such compositions is mercuric thiocyanate or "pharaoh's serpents" which, when ignited, forms a voluminous ash that resembles a moving serpent. Other compositions have been formulated which combust to form adherent, tough insulating foams that resist further burning and act to insulate and protect the underlying substrate. These formulations have found wide commercial use in fire retardant paints and mastics.
More recently, additives have been incorporated into molding resins which render them intumescent and flame retardant. In U.S. Pat. Nos. 3,936,416 and 4,201,705 there are described polyolefin compositions containing melammonium polyphosphates and phosphate esters which are flame retarded. Upon combustion, a tough, insulating char forms at the surface of the molded article which resists further burning and acts to protect the bulk of the polyolefin resin from further burning.
As is well known in the art, the behavior of flame retardant additives in resin formulations varies greatly with the nature of polymeric substrate. This is particularly true with intumescent compositions since the rapid formation of the protective char layer is highly dependent upon such factors as the combustion temperature and the viscosity of the melt formed by the burning substrate. Other considerations that may also come into play even where the intumescent behavior is optimum include the effect of the additive on the physical properties, color and molding characteristics of the base resin. The development of intumescent additives for use in flame retarding resins thus remains a highly empirical art wherein predictability of behavior is rare to non-existent, and the art has largely concentrated on the development of highly specific additive combinations for particular resins and end-uses.
The development of an intumescent additive combination which exhibits a greater latitude in dispersability and char-forming character and thus capable of being formulated for use in a wider variety of dissimilar resins would thus be a useful advance in the flame retardant art.